The present invention pertains to the field of producing near fragment-free access openings, more particularly to the field of using explosive materials that produce near-fragment free openings in hardened structures such as metal shipping containers and most particularly to the field of using explosive material to produce near-fragment free openings in hardened containers that house agents or substances that must not be overly disturbed.
Bomb squad technicians regularly deal with packages that need to be opened for immediate inspection or remotely in locations where heavy cutting tools may not be assembled or time is of the essence. In order to reduce the risks associated with opening such packages, technicians primarily use either robotic tools or explosive access tools that can be initiated from a distance. For certain types of packages or containers, robotic access tools, which often lack precision, power, and are cumbersome, cannot be employed. For these types of packages, such as sea-land containers, metal drums, or other hardened containers, explosive access tools are the only option.
Various explosive tools have been employed for this purpose. One technique is to employ a linear shaped charge to create an opening in the hardened container. These shaped charges comprise a chevron shaped metallic casing, which is usually copper, aluminum, or lead, that contains a quantity of high explosives. The charge cuts the hardened container by accelerating each side of the chevron shaped wedge into each other, forming a high velocity metal jet. However, this technique, like merely using high explosives to directly cut into hardened targets, produces many fragments, which are capable of overly disturbing the contents within the container.
In order to alleviate this fragmentation problem, a device commonly know as the Magic Cube™ was developed and disclosed in U.S. Pat. No. 6,220,166. This device comprises a sheet explosive that is initiated at four different points and a buffer material, made up of three sheets of stacked, low density material, such as polyethylene foam which is placed between the explosive and the target. Various types of tapes and adhesives are required in order to combine these elements and affix the final device to the target. While the device does alleviate the fragmentation problem discussed above under certain circumstances, it does have several problems associated with its intended use. First, due to the complexity of the device, any particular embodiment is designed to operate on only one range of specific wall thickness. Second, also due to the complexity of the device, it is relatively expensive.
Another device commonly known as the X-Cutter™ was developed, disclosed and claimed in U.S. Pat. No. 6,865,990 to alleviate the fragmentation problem. This device comprises a flexible material, preferably in a mostly square shape, having substantially orthogonal grooves scored into one side. An explosive charge, usually in the form of sheet explosives, is cut to fit the side opposite the grooves, in substantially the same shape as the grooves, without extending beyond the periphery of the flexible material. An initiating means is connected to the explosive charge so that upon initiation, the grooves focus the explosive charge so that a plurality of petals cantilevered from the target plate are formed in the target material, substantially between the ends of the grooves, to define a fragment-free opening in the target material. Again, this device does alleviate the fragmentation problem discussed above under most conditions, but it does not have the simplicity of fabrication of the invention herein presented. The X-Cutter™ needs the grooves to be placed in the flexible material in a machine shop.
Therefore, it is desired to provide an explosive access tool that produces little fragmentation, is inexpensive, simple to fabricate, and can be used on containers made of steel, having various shapes and of varying wall thickness.